Re: [PATCH 1/2] rust_binder: check ownership before using vma

["Danilo Krummrich" <dakr@kernel.org>]

On Tue Feb 17, 2026 at 9:12 PM CET, Alice Ryhl wrote:
> On Tue, Feb 17, 2026 at 4:13 PM Danilo Krummrich <dakr@kernel.org> wrote:
>>
>> On Tue Feb 17, 2026 at 3:22 PM CET, Alice Ryhl wrote:
>> > When installing missing pages (or zapping them), Rust Binder will look
>> > up the vma in the mm by address, and then call vm_insert_page (or
>> > zap_page_range_single). However, if the vma is closed and replaced with
>> > a different vma at the same address, this can lead to Rust Binder
>> > installing pages into the wrong vma.
>> >
>> > By installing the page into a writable vma, it becomes possible to write
>> > to your own binder pages, which are normally read-only. Although you're
>> > not supposed to be able to write to those pages, the intent behind the
>> > design of Rust Binder is that even if you get that ability, it should not
>> > lead to anything bad. Unfortunately, due to another bug, that is not the
>> > case.
>> >
>> > To fix this, I will store a pointer in vm_private_data and check that
>> > the vma returned by vma_lookup() has the right vm_ops and
>> > vm_private_data before trying to use the vma. This should ensure that
>> > Rust Binder will refuse to interact with any other VMA. I will follow up
>> > this patch with more vma abstractions to avoid this unsafe access to
>> > vm_ops and vm_private_data, but for now I'd like to start with the
>> > simplest possible fix.
>>
>> I suggest to use imperative mood instead.
>
> How do you propose to reword "I will follow up this patch with"?

To fix this, store a pointer in vm_private_data and check [...]. Subsequent work
will follow-up this patch with [...], but for now start with the simplest
possible fix.

>> > +        // This pointer is only used for comparison - it's not dereferenced.
>> > +        //
>> > +        // SAFETY: We own the vma, and we don't use any methods on VmaNew that rely on
>> > +        // `vm_private_data`.
>> > +        unsafe { (*vma.as_ptr()).vm_private_data = self as *const Self as *mut c_void };
>>
>> Maybe use from_ref(self).cast_mut().cast::<c_void>() instead?
>
> Honestly I think this one is easier to read as-is.

I remember this series: https://lore.kernel.org/all/20250615-ptr-as-ptr-v12-0-f43b024581e8@gmail.com/

It talks about enabling clippy::ref_as_ptr and I think we have it enabled, does
this not apply here?